Method and apparatus for secure communication and determining secret information

ABSTRACT

A method of secure communication in a transmitter, includes determining a method of generating a training sequence that is shared with a receiver. The method further includes generating the training sequence based on the method of generating the training sequence, and secret information. The method further includes communicating with the receiver based on channel information derived from the training sequence.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit under 35 U.S.C. §119(a) of KoreanPatent Application No. 10-2012-0068556, filed on Jun. 26, 2012, in theKorean Intellectual Property Office, the entire disclosure of which isincorporated herein by reference of all purposes.

BACKGROUND

1. Field

The following description relates to a method and apparatus for securecommunication and determining secret information.

2. Description of Related Art

In a wireless communication system, establishing secure communicationbetween communication units is of paramount significance. Theestablishing of the secure communication may be achieved by exchanging akey that includes a user interaction, for example, a user inputting apasscode, such as a password or a personal identification number (PIN),in a single or dual communication unit.

A method of secure communication may include a method of dataencryption. The method of the data encryption may include conducting anauthentication and a key exchange, and protecting data using at leastone set key. For example, after setting an encryption key, a transmittermay encrypt data of secure communication using the encryption key and anencryption method, and may transmit the encrypted data to a receiver.The receiver may decrypt the encrypted data to the original data using adecryption key and a decryption method. Provided that a third party isunaware of a decryption method and a decryption key, data transmittedbetween a transmitter and a receiver may be protected, even if the datais exposed.

Also, a system of secure communication may include a public keyinfrastructure (PKI). The system of the secure communication is complex,and encrypts data through a public key method and a digital signature.The public key includes an encryption key and a decryption key, and auser is authenticated through the digital certificate.

SUMMARY

In one general aspect, there is provided a method of securecommunication in a transmitter, the method including determining amethod of generating a training sequence that is shared with a receiver.The method further includes generating the training sequence based onthe method of generating the training sequence, and secret information.The method further includes communicating with the receiver based onchannel information derived from the training sequence.

In another general aspect, there is provided a method of determiningsecret information in a transmitter, the method including transmitting,to a receiver, a hash value of channel information in the transmitter.The method further includes receiving, from the receiver, a responsecorresponding to the hash value. The method further includes determiningthe secret information based on the channel information and theresponse.

In still another general aspect, there is provided a method ofdetermining secret information in a receiver, the method includingreceiving, from a transmitter, a hash value of the transmitter. Themethod further includes transmitting, to the transmitter, a responsecorresponding to the received hash value based on a comparison of thereceived hash value and a hash value of channel information in thereceiver. The method further includes determining secret informationbased on the channel information and the comparison.

In yet another general aspect, there is provided a transmitter thatperforms secure communication, the transmitter including an agreeingunit configured to determine a method of generating a training sequencethat is shared with a receiver. The transmitter further includes agenerating unit configured to generate the training sequence based onthe method of generating the training sequence, and secret information.The transmitter further includes a communicating unit configured tocommunicate with the receiver based on channel information derived fromthe training sequence.

In still another general aspect, there is provided a transmitter thatdetermines secret information, the transmitter including a communicatingunit configured to transmit, to a receiver, a hash value of channelinformation in the transmitter, and receive, from the receiver, aresponse corresponding to the hash value. The transmitter furtherincludes a determining unit configured to determine the secretinformation based on the channel information and the response.

Other features and aspects will be apparent from the following detaileddescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a system that performssecure communication.

FIG. 2 is a diagram illustrating an example of a transmitter thatperforms secure communication.

FIG. 3 is a diagram illustrating an example of a transmitter thatdetermines secret information.

FIG. 4 is a flowchart illustrating an example of a method of performingsecure communication in a transmitter and a receiver.

FIG. 5 is a flowchart illustrating an example of a method of determiningsecret information in a transmitter.

FIG. 6 is a flowchart illustrating an example of a method of determiningsecret information in a receiver.

DETAILED DESCRIPTION

The following detailed description is provided to assist the reader ingaining a comprehensive understanding of the methods, apparatuses,and/or systems described herein. However, various changes,modifications, and equivalents of the systems, apparatuses and/ormethods described herein will be apparent to one of ordinary skill inthe art. Also, descriptions of functions and constructions that are wellknown to one of ordinary skill in the art may be omitted of increasedclarity and conciseness.

Throughout the drawings and the detailed description, the same referencenumerals refer to the same elements. The drawings may not be to scale,and the relative size, proportions, and depiction of elements in thedrawings may be exaggerated of clarity, illustration, and convenience.

The features described herein may be embodied in different forms, andare not to be construed as being limited to the examples describedherein. Rather, the examples described herein have been provided so thatthis disclosure will be thorough and complete, and will convey the fullscope of the disclosure to one of ordinary skill in the art.

FIG. 1 is a diagram illustrating an example of a system that performssecure communication. Referring to FIG. 1, the system includes atransmitter 110 and a receiver 120. The system may include, for example,a cellular environment, a wireless network environment, and/or otherenvironments known to one of ordinary skill in the art.

The transmitter 110 and the receiver 120 communicate with each other,using a predetermined secure channel (e.g., a wireless channel) in aphysical layer. The transmitter 110 and the receiver 120 generate ordetermine secret information based on channel information shared betweenthe transmitter 110 and the receiver 120. For example, the channelinformation may include gain information, amplitude information,information of an area occupied in a channel graph, and/or otherphysical information known to one of ordinary skill in the art, of thechannel between the transmitter 110 and the receiver 120. Thetransmitter 110 and the receiver 120 may share the channel informationwith each other in advance, and/or the secure channel. In this example,the secret information may include a secret key that may be sharedbetween the transmitter 110 and the receiver 120 in advance.

The transmitter 110 and the receiver 120 may generate the secretinformation to be unknown to a third terminal 130 between thetransmitter 110 and the receiver 120, based on a physical property(e.g., the channel information shared between the transmitter 110 andthe receiver 120) of the physical layer. The transmitter 110 and thereceiver 120 may provide the generated secret information to an upperlayer, and the upper layer may encrypt data of the upper layer based onthe provided secret information.

Also, the transmitter 110 and the receiver 120 may be provided with thesecret information. For example, the transmitter 110 and the receiver120 may share the secret information with each other through the securechannel.

The transmitter 110 and the receiver 120 determine whether channelinformation of the transmitter 110 and channel information of thereceiver 120 are equal to each other. For example, the transmitter 110and the receiver 120 may determine whether the channel information ofthe transmitter 110 and the channel information of the receiver 120 areequal to each other based on respective hash values. In more detail, thetransmitter 110 may quantize the channel information of the transmitter,and may map the quantized channel information to a hash value, using ahash function. In other words, the transmitter 110 may convert thechannel information to an integer that represents the channelinformation in bits, and may match the converted channel information tothe hash value, using the hash function. The hash function may refer toa function of generating a type of a short electronic fingerprint basedon random data, and may generate the hash value by cutting,substituting, changing locations, and/or other operations known to oneof ordinary skill in the art. The receiver 120 may perform similaroperations as those of the transmitter 110.

In this example, the receiver 120 may receive the hash value of thechannel information in the transmitter 110, and may compare the hashvalue of the channel information in the transmitter 110 to a hash valueof the channel information in the receiver 120. When the hash value ofthe channel information in the transmitter 110 is determined to be equalto the hash value of the channel information in the receiver 120, thereceiver 120 determines that the channel information of the transmitter110 and the channel information of the receiver 120 are equal to eachother. When the hash value of the channel information in the transmitter110 is determined to differ from the hash value of the channelinformation in the receiver 120, the receiver 120 changes the channelinformation in the receiver 120 based on a predetermined method, andmaps the changed channel information to a new hash value to betransmitted to the transmitter 110. The transmitter 110 may performsimilar operations as those of the receiver 120.

In this example, when the transmitter 110 receives the new hash valuefrom the receiver 120, the transmitter 110 may change the channelinformation of the transmitter 110 based on the predetermined method,map the changed channel information to a new hash value, and compare thenew hash value mapped by the transmitter 110 to the new hash valuereceived from the receiver 120. The receiver 120 may perform similaroperations as those of the transmitter 110.

The transmitter 110 and the receiver 120 may perform such a processrepeatedly until the hash value of the channel information in thetransmitter 110 is equal to the hash value of the channel information inthe receiver 120, which indicates that the channel information of thetransmitter 110 and the channel information of the receiver 120 areequal to each other. When the channel information of the transmitter 110and the channel information of the receiver 120 are determined to beequal to each other, the transmitter 110 and the receiver 120 maytransmit, to each other, a response indicating that the hash value ofthe channel information in the transmitter 110 is equal to the hashvalue of the channel information in the receiver 120. In this example,the transmitter 110 and the receiver 120 determine the secretinformation based on (e.g., to be) the channel information sharedbetween the transmitter 110 and the receiver 120. The above process willbe described with reference to FIGS. 5 and 6.

The transmitter 110 and the receiver 120 determine (e.g., agree on) amethod of generating a unique training sequence, prior to generatingrespective unique training sequences. In wireless communication, theunique training sequence may include, for example, a pilot, a reference,or a preamble that is used to share channel information. The transmitter110 and the receiver 120 may exchange or synchronize the determinedmethod of generating a unique training sequence with each other.

When the secret information is determined by the transmitter 110 and thereceiver 120, respectively, the transmitter 110 and the receiver 120 maymatch (e.g., set to be equal) the secret information of the transmitter110 to the secret information of the receiver 120, prior to thedetermining of the method of generating the unique training sequence.Conversely, when the secret information is shared between thetransmitter 110 and the receiver 120 prior to the determining of themethod of generating the unique training sequence, the matching of thesecret information may be unnecessary. The transmitter 110 and thereceiver 120 may determine (e.g., agree on) secret information among thesecret information determined by the transmitter 110 and the receiver120, to be used to generate a unique training sequence.

The transmitter 110 and the receiver 120 generate the respective uniquetraining sequences that are equal to each other based on the secretinformation determined by the transmitter 110 and the receiver 120, thedetermined method of generating a unique training sequence, and a publictraining sequence. The public training sequence may include a pilot, areference, or a preamble that is used in a wireless communicationenvironment and shared between terminals including the transmitter 110and the receiver 120 prior to the generating of the unique trainingsequences. For example, the transmitter 110 and the receiver 120 maygenerate the respective unique training sequences by inputting thesecret information and the public training sequence in a function.

The transmitter 110 and the receiver 120 may share or exchange therespective generated unique training sequences with each other, e.g.,through the secure channel. For example, the transmitter 110 maytransmit, to the receiver 120, the unique training sequence generated bythe transmitter 110, e.g., through the secure channel. In response, thereceiver 120 may transmit, to the transmitter 110, a confirmation ofsafe receipt of the unique training sequence generated by thetransmitter 110.

The transmitter 110 and the receiver 120 perform secure communicationwith each other based on the respective generated unique trainingsequences, using a new channel in the physical layer. The above processwill be described with reference to FIG. 4. For example, since thetransmitter 110 and the receiver 120 use the respective generativeunique training sequences unknown to the third terminal 130, the thirdterminal 130 may not create a channel, or obtain channel information,between the transmitter 110 and the third terminal 130, and between thereceiver 120 and the third terminal 130. Accordingly, the transmitter110 and the receiver 120 may prevent communication content between thetransmitter 110 and the receiver 120 from being exposed to the thirdterminal 130, by not exposing, e.g., a packet header to the thirdterminal 130.

Further, by generating the respective unique training sequences based onthe secret information determined by the transmitter 110 and thereceiver 120, the transmitter 110 and the receiver 120 may perform thesecure communication with each other, without an additional encryptionprocess based on the secret information. Also, since the transmitter 110and the receiver 120 may not have to perform an additional encryptionprocess, a communication environment between the transmitter 110 and thereceiver 120 may be improved, and an amount of energy expended during acommunication process between the transmitter 110 and the receiver 120may be reduced. If an additional encryption process is performed basedon the secret information, the secret information may be used to protecta channel in the physical layer, and to perform secure communication inthe upper layer.

In another example, each of the transmitter 110 and the receiver 120 maychange an order of data included in the public training sequence basedon the secure information, and may generate the unique training sequencefurther based on the changed order of the data included in the publictraining sequence. For example, each of the transmitter 110 and thereceiver 120 may shuffle the data included in the public trainingsequence, and may generate the unique training sequence further based onthe shuffled data.

For example, each of the transmitter 110 and the receiver 120 may changean order of data included in a public training sequence L_(−26.26)={1,1, . . . , −1, . . . , 1} defined in Institute of Electrical andElectronics Engineers (IEEE) 802.11a, and may generate the uniquetraining sequence further based on the changed order of the dataincluded in the public training sequence. In this example, each of thetransmitter 110 and the receiver 120 may generate 2⁵² different uniquetraining sequences based on the public training sequence and secretinformation that includes 52 bits of data as included in the publictraining sequence. If the generated unique training sequence isinappropriate for a communication environment, each of the transmitter110 and the receiver 120 may re-generate the unique training sequence.

In still another example, each of the transmitter 110 and the receiver120 may extract the data from the public training sequence selectively,and may generate the unique training sequence further based on theextracted data. In yet another example, each of the transmitter 110 andthe receiver 120 may combine data of the secret information and the dataof the public training sequence, and may generate the unique trainingsequence further based on the combination. In still another example,each of the transmitter 110 and the receiver 120 may generate the uniquetraining sequence further based on index information of the publictraining sequence.

Since the unique training sequence is used as a secret value between thetransmitter 110 and the receiver 120, the transmitter 110 and thereceiver 120 may prevent the third terminal 130 from generating achannel equal to a new channel generated by the transmitter 110 and thereceiver 120 using the unique training sequence. Accordingly, thetransmitter 110 may prevent the third terminal 130 from obtainingcommunication content between the transmitter 110 and the receiver 120that is communicated based on the unique training sequence.

Each of the transmitter 110 and the receiver 120 derives new channelinformation between the transmitter 110 and the receiver 120 based onthe generated unique training sequence. The transmitter 110 and thereceiver 120 perform the secure communication with each other based onthe derived new channel information, using the new channel in thephysical layer. When the secret information is determined by and sharedbetween the transmitter 110 and the receiver 120, the new channelinformation derived by the transmitter 110 may be equal to the newchannel information derived by the receiver 120.

When the secure communication is unnecessary between the transmitter 110and the receiver 120, the transmitter 110 and the receiver 120 performscommunication based on channel information derived from the publictraining sequence. That is, the transmitter 110 and the receiver 120 mayperform the secure communication only in a section requiring the securecommunication.

FIG. 2 is a diagram illustrating an example of a transmitter 210 thatperforms secure communication. Referring to FIG. 2, the transmitter 210includes an agreeing unit 220, a generating unit 230, and acommunicating unit 240.

The agreeing unit 220 determines (e.g., agrees, with a receiver, on) amethod of generating a unique training sequence based on secretinformation included in the agreeing unit 220. This determination mayinclude determining an agreement between the transmitter 210 and thereceiver on the secure communication as a whole. For example, theagreeing unit 220 may further determine (e.g., agree on) secretinformation among secret information included in the transmitter 210 andthe receiver, to be used to generate a unique training sequence.Accordingly, the transmitter 210 and the receiver generate respectiveunique training sequences based on the secret information included inthe transmitter 210 and the receiver, the determined method ofgenerating a unique training sequence, and a public training sequence.When the transmitter 210 and the receiver determine the secretinformation included in the transmitter 210 and the receiver,respectively, the transmitter 210 and the receiver may match (e.g., setto be equal) the secret information included in the transmitter 210 tothe secret information included in the receiver, prior to thedetermining of the method of generating the unique training sequence.

The generating unit 230 generates the unique training sequence based onthe secret information included in the agreeing unit 220, the determinedmethod of generating a unique training sequence, and the public trainingsequence. In wireless communication, the unique training sequence mayinclude, for example, a pilot, a reference, or a preamble. Accordingly,the transmitter 210 performs the secure communication with the receiverbased on the generated unique training sequence.

For example, the generating unit 230 may change an order of dataincluded in the public training sequence, and may generate the uniquetraining sequence based on the changed order of the data included in thepublic training sequence. In another example, the generating unit 230may extract the data from the public training sequence selectively, maygenerate the unique training sequence based on the extracted data. Instill another example, the generating unit 230 may combine data includedin the secret information and the data included in the public trainingsequence, and may generate the unique training sequence based on thecombination.

The communicating unit 240 communicates with the receiver based on thegenerated unique training sequence. In more detail, the communicatingunit 240 performs the secure communication with the receiver based onnew channel information between the transmitter 210 and the receiverthat is derived from the generated unique training sequence.

When the secure communication is unnecessary between the transmitter 210and the receiver, the communicating unit 240 may communicate with thereceiver based on the public training sequence, namely, the channelinformation derived from the public training sequence. That is, thetransmitter 210 and the receiver may perform the secure communicationonly in a section requiring the secure communication.

FIG. 3 is a diagram illustrating an example of a transmitter 310 thatdetermines secret information. Referring to FIG. 3, the transmitter 310includes a generating unit 320, a communicating unit 330, a changingunit 340, and a determining unit 350.

The generating unit 320 generates channel information of the transmitter310 in a form of a hash value. In more detail, the generating unit 320may quantize the channel information, and may map the quantized channelinformation to the hash value, using a hash function. In other words,the generating unit 320 may convert the channel information to aninteger in bits, and may apply the converted channel information in thehash function to generate the hash value. When the changing unit 340changes the channel information, the generating unit 320 applies thechanged channel information in the hash function to generate a new hashvalue.

The communicating unit 330 transmits, to a receiver, the generated hashvalue. Further, the communicating unit 330 receives, from the receiver,a response corresponding to the hash value. The response may indicatewhether the transmitted hash value of the transmitter 310 is equal to ahash value (of channel information) of the receiver, or may include thehash value of the receiver. If the communicating unit 330 receives, fromthe receiver, the hash value of the receiver, the communicating unit 330may recognize that the transmitted hash value of the transmitter 310differs from the hash value of the receiver, despite an absence of theresponse indicating whether the transmitted hash value of thetransmitter 310 is equal to the hash value of the receiver.

The changing unit 340 also receives, from the receiver, the responsecorresponding to the hash value. If the changing unit 340 receives theresponse indicating that the transmitted hash value of the transmitter310 differs from the hash value of the receiver, the changing unit 340changes the channel information of the transmitter 310 based on apredetermined method. For example, the predetermined method may includea method of dividing the channel information, a method of generating adata section of a predetermined location in a form of new channelinformation, and/or other methods known to one of ordinary skill in theart. The generating unit 320 may generate the new hash value based onthe changed channel information.

If the changing unit 340 receives the response indicating that thetransmitted hash value of the transmitter 310 differs from the hashvalue of the receiver, the changing unit 340 may change a predeterminedlength among a total length of data of the channel information of thetransmitter 310. For example, if the changing unit 340 receives theresponse indicating that the transmitted hash value of the transmitter310 differs from the hash value of the receiver, the changing unit 340may cut the predetermined length among the total length of the data ofthe channel information of the transmitter 310. The generating unit 320may generate the new hash value based on a remainder of the cut channelinformation of the transmitter 310.

The determining unit 350 also receives, from the receiver, the responsecorresponding to the hash value, and determines the secret informationbased on the channel information of the transmitter 310 and theresponse. For example, when the determining unit 350 receives theresponse indicating that the transmitted hash value of the transmitter310 is equal to the hash value of the receiver, the determining unit 350determines the secret information to be the channel information of thetransmitter 310. In this example, the determining unit 350 may determinethe secret information to be the channel information quantized by thegenerating unit 320.

If the generating unit 320 generates the new hash value based on thechanged channel information of the transmitter 310, and the responseincludes the hash value of the receiver, the determining unit 350determines whether the new hash value is equal to the hash value of thereceiver. If the new hash value is equal to the hash value of thereceiver, the determining unit 350 determines the secret information tobe the changed channel information of the transmitter 310.

FIG. 4 is a flowchart illustrating an example of a method of performingsecure communication in a transmitter 410 and a receiver 420. Inoperation 430, the transmitter 410 and the receiver 420 determine (e.g.,agree on) a method of generating a unique training sequence. Thetransmitter 410 and the receiver 420 may further determine (e.g., agreeon) secret information, among secret information included in thetransmitter 410 and the receiver 420, to be used to generate a uniquetraining sequence. The transmitter 410 and the receiver 420 may furthershare the secret information with each other in advance. The transmitter410 and the receiver 420 may further generate or determine the secretinformation of the transmitter 410 and the receiver 420, respectively,and may match (e.g., set to be equal) the secret information of thetransmitter 410 to the secret information of the receiver 420.

In operations 440 and 450, the transmitter 410 and the receiver 420generate respective unique training sequences based on the secretinformation of the transmitter 410 and the receiver 420, the determinedmethod of generating a unique training sequence, and a public trainingsequence. The unique training sequence may include, for example, apilot, a reference, or a preamble. The transmitter 410 and the receiver420 may further change an order of data included in the public trainingsequence, or may extract the data from the public training sequenceselectively, to generate the unique training sequence. The transmitter410 and the receiver 420 may further combine data included in the secretinformation and the data included in the public training sequence, togenerate the unique training sequence. The transmitter 410 and thereceiver 420 may further input the secret information and the publictraining sequence in a function, to generate the unique trainingsequence. When the secret information of the transmitter 410 is matchedor equal to the secret information of the receiver 420, the transmitter410 and the receiver 420 generate the respective unique trainingsequences that are matched or equal to each other.

The transmitter 410 and the receiver 420 may share or exchange therespective generated unique training sequences with each other, e.g.,through a secure channel. For example, the transmitter 410 may transmit,to the receiver 420, the unique training sequence generated by thetransmitter 410, e.g., through the secure channel. In response, thereceiver 420 may transmit, to the transmitter 410, a confirmation ofsafe receipt of the unique training sequence generated by thetransmitter 410.

In operations 460 and 470, each of the transmitter 410 and the receiver420 derives channel information from the generated unique trainingsequence. When the unique training sequence of the transmitter 410 ismatched or equal to the unique training sequence of the receiver 420,the transmitter 410 and the receiver 420 generate the respective channelinformation that are matched or equal to each other.

In operation 480, the transmitter 410 and the receiver 420 communicatewith each other, using the derived channel information, and a newchannel in a physical layer. For example, the transmitter 410 and thereceiver 420 may further form the new channel, using the unique trainingsequence, and exchange data with each other through the new channel.When the secure communication between the transmitter 410 and thereceiver 420 is unnecessary, the transmitter 410 and the receiver 420communicate with each other based on channel information derived fromthe public training sequence.

FIG. 5 is a flowchart illustrating an example of a method of determiningsecret information in a transmitter. In operation 510, the transmittergenerates channel information in a form of a hash value. The transmittermay further quantize the channel information, and generate the quantizedchannel information in the form of the hash value.

In operation 520, the transmitter transmits the generated hash value tothe receiver. If the channel information of the transmitter changes, thetransmitter may further re-generate the hash value based on the changedchannel information, and transmit the re-generated hash value to thereceiver.

In operation 530, the transmitter receives a response corresponding tothe transmitted hash value from the receiver. For example, the responsemay indicate whether the transmitted hash value of the transmitter isequal to a hash value (of channel information) of the receiver, or mayinclude the hash value of the receiver. If the transmitter receives thehash value of the receiver, the transmitter may further recognize thatthe transmitted hash value of the transmitter differs from the hashvalue of the receiver, despite an absence of the response indicatingwhether the transmitted hash value of the transmitter is equal to thehash value of the receiver.

In operation 540, the transmitter determines whether the responseindicates that the transmitted hash value of the transmitter is equal tothe hash value of the receiver. If the response indicates that thetransmitted hash value of the transmitter is equal to the hash value ofthe receiver, the method continues in operation 550. Otherwise, themethod continues in operation 590.

In operation 550, the transmitter changes the channel information of thetransmitter in a form of the hash value based on a predetermined method.For example, the predetermined method may include a method of dividingthe channel information, a method of generating a data section of apredetermined location in a form of new channel information, and/orother methods known to one of ordinary skill in the art.

In operation 560, the transmitter determines whether the changed hashvalue of the transmitter is equal to the hash value of the receiver. Ifthe changed hash value of the transmitter is equal to the hash value ofthe receiver, the method continues in operation 570. Otherwise, themethod continues in operation 580.

In operation 570, the transmitter transmits, to the receiver, a responseindicating that the changed hash value of the transmitter is equal tothe hash value of the receiver.

In operation 580, the transmitter re-changes the channel information ofthe transmitter in a form of the hash value based on the predeterminedmethod. The method returns to operation 520.

In operation 590, the transmitter determines the secret informationbased on the channel information of the transmitter. The transmitter maydetermine that the channel information or the changed channelinformation, of the transmitter, is the secret information. Thetransmitter may further determine that the quantized channel informationof the transmitter is the secret information. Since an order in whichsuch operations are performed may not be limited to those suggested inoperations 570 and 590, operation 590 may be performed prior tooperation 570, or may be performed simultaneously.

As such, the transmitter may match (e.g., set to be equal) the channelinformation of the transmitter to the channel information shared by thereceiver by repeating a process of generating the channel information ofthe transmitter in the form of the hash value, and changing the channelinformation of the transmitter in the form of the hash value until thehash value of the transmitter is determined to be equal to the hashvalue of the receiver.

FIG. 6 is a flowchart illustrating an example of a method of determiningsecret information in a receiver. In operation 610, the receivergenerates channel information in a form of a hash value. The receivermay further quantize the channel information, and generate the quantizedchannel information in the form of the hash value.

In operation 620, the receiver receives, from a transmitter, a hashvalue to which channel information of the transmitter is applied. Sincean order in which such operations are performed may not be limited tothose suggested in operations 610 and 620, operation 620 may beperformed prior to operation 610, or may be performed simultaneously.

In operation 630, the receiver determines whether the hash valuereceived from the transmitter is equal to the hash value generated bythe receiver. If the hash value received from the transmitter is notequal to the hash value generated by the receiver, the method continuesin operation 640. Otherwise, the method continues in operation 690.

In operation 640, the receiver changes the channel information of thereceiver based on a predetermined method, and re-generates the hashvalue based on the changed channel information. For example, thereceiver may change (e.g., cut) a predetermined length among a totallength of data of the channel information to change the channelinformation, and may re-generate the hash value based on the changedchannel information applied in a hash function.

In operation 650, the receiver transmits, to the transmitter, there-generated hash value. The receiver may further transmit, togetherwith the re-generated hash value, a response indicating that the hashvalue received from the transmitter is equal to, or differs from, thehash value re-generated by the receiver.

In operation 660, the receiver receives, from the transmitter, aresponse corresponding to the transmitted hash value, and determineswhether the response indicates that the hash value of the transmitter isequal to the hash value transmitted by the receiver. If the responseindicates that the hash value of the transmitter is not equal to thehash value transmitted by the receiver, the method continues inoperation 670. Otherwise, the method continues in operation 700.

In operation 670, the receiver changes the channel information of thereceiver based on the predetermined method, and re-generates the hashvalue based on the changed channel information.

In operation 680, the receiver determines whether the hash valuereceived from the transmitter is equal to the hash value re-generated bythe receiver. If the hash value received from the transmitter is equalto the hash value re-generated by the receiver, the method continues inoperation 690. Otherwise, the method returns to operation 640.

In operation 690, the receiver transmits, to the transmitter, a responseindicating that the hash value received from the transmitter is equal tothe hash value generated or re-generated by the receiver.

In operation 700, the receiver determines the secret information basedon the channel information of the receiver. The receiver may furtherdetermine the channel information or the changed channel information, ofthe receiver, to be secret information. The receiver may furtherdetermine the quantized channel information to be the secretinformation. Since an order in which such operations are performed maynot be limited to those suggested in operations 660 and 670, operation670 may be performed prior to operation 660, or may be performedsimultaneously.

As such, the receiver may match (e.g., set to be equal) the channelinformation of the receiver to the channel information shared by thetransmitter by repeating a process of generating the channel informationof the receiver in the form of the hash value, and changing the channelinformation of the receiver in the form of the hash value until the hashvalue of the receiver is determined to be equal to the hash value of thetransmitter.

The various units and methods described above may be implemented usingone or more hardware components, one or more software components, or acombination of one or more hardware components and one or more softwarecomponents.

A hardware component may be, of example, a physical device thatphysically performs one or more operations, but is not limited thereto.Examples of hardware components include microphones, amplifiers,low-pass filters, high-pass filters, band-pass filters,analog-to-digital converters, digital-to-analog converters, andprocessing devices.

A software component may be implemented, of example, by a processingdevice controlled by software or instructions to perform one or moreoperations, but is not limited thereto. A computer, controller, or othercontrol device may cause the processing device to run the software orexecute the instructions. One software component may be implemented byone processing device, or two or more software components may beimplemented by one processing device, or one software component may beimplemented by two or more processing devices, or two or more softwarecomponents may be implemented by two or more processing devices.

A processing device may be implemented using one or more general-purposeor special-purpose computers, such as, of example, a processor, acontroller and an arithmetic logic unit, a digital signal processor, amicrocomputer, a field-programmable array, a programmable logic unit, amicroprocessor, or any other device capable of running software orexecuting instructions. The processing device may run an operatingsystem (OS), and may run one or more software applications that operateunder the OS. The processing device may access, store, manipulate,process, and create data when running the software or executing theinstructions. For simplicity, the singular term “processing device” maybe used in the description, but one of ordinary skill in the art willappreciate that a processing device may include multiple processingelements and multiple types of processing elements. For example, aprocessing device may include one or more processors, or one or moreprocessors and one or more controllers. In addition, differentprocessing configurations are possible, such as parallel processors ormulti-core processors.

A processing device configured to implement a software component toperform an operation A may include a processor programmed to runsoftware or execute instructions to control the processor to performoperation A. In addition, a processing device configured to implement asoftware component to perform an operation A, an operation B, and anoperation C may include various configurations, such as, of example, aprocessor configured to implement a software component to performoperations A, B, and C; a first processor configured to implement asoftware component to perform operation A, and a second processorconfigured to implement a software component to perform operations B andC; a first processor configured to implement a software component toperform operations A and B, and a second processor configured toimplement a software component to perform operation C; a first processorconfigured to implement a software component to perform operation A, asecond processor configured to implement a software component to performoperation B, and a third processor configured to implement a softwarecomponent to perform operation C; a first processor configured toimplement a software component to perform operations A, B, and C, and asecond processor configured to implement a software component to performoperations A, B, and C, or any other configuration of one or moreprocessors each implementing one or more of operations A, B, and C.Although these examples refer to three operations A, B, C, the number ofoperations that may implemented is not limited to three, but may be anynumber of operations required to achieve a desired result or perform adesired task.

Software or instructions that controls a processing device to implementa software component may include a computer program, a piece of code, aninstruction, or some combination thereof, that independently orcollectively instructs or configures the processing device to performone or more desired operations. The software or instructions may includemachine code that may be directly executed by the processing device,such as machine code produced by a compiler, and/or higher-level codethat may be executed by the processing device using an interpreter. Thesoftware or instructions and any associated data, data files, and datastructures may be embodied permanently or temporarily in any type ofmachine, component, physical or virtual equipment, computer storagemedium or device, or a propagated signal wave capable of providinginstructions or data to or being interpreted by the processing device.The software or instructions and any associated data, data files, anddata structures also may be distributed over network-coupled computersystems so that the software or instructions and any associated data,data files, and data structures are stored and executed in a distributedfashion.

For example, the software or instructions and any associated data, datafiles, and data structures may be recorded, stored, or fixed in one ormore non-transitory computer-readable storage media. A non-transitorycomputer-readable storage medium may be any data storage device that iscapable of storing the software or instructions and any associated data,data files, and data structures so that they can be read by a computersystem or processing device. Examples of a non-transitorycomputer-readable storage medium include read-only memory (ROM),random-access memory (RAM), flash memory, CD-ROMs, CD-Rs, CD+Rs, CD-RWs,CD+RWs, DVD-ROMs, DVD-Rs, DVD+Rs, DVD-RWs, DVD+RWs, DVD-RAMs, BD-ROMs,BD-Rs, BD-R LTHs, BD-REs, magnetic tapes, floppy disks, magneto-opticaldata storage devices, optical data storage devices, hard disks,solid-state disks, or any other non-transitory computer-readable storagemedium known to one of ordinary skill in the art.

Functional programs, codes, and code segments of implementing theexamples disclosed herein can be easily constructed by a programmerskilled in the art to which the examples pertain based on the drawingsand their corresponding descriptions as provided herein.

As a non-exhaustive illustration only, a terminal described herein maybe a mobile device, such as a cellular phone, a personal digitalassistant (PDA), a digital camera, a portable game console, an MP3player, a portable/personal multimedia player (PMP), a handheld e-book,a portable laptop PC, a global positioning system (GPS) navigationdevice, a tablet, a sensor, or a stationary device, such as a desktopPC, a high-definition television (HDTV), a DVD player, a Blue-rayplayer, a set-top box, a home appliance, or any other device known toone of ordinary skill in the art that is capable of wirelesscommunication and/or network communication.

While this disclosure includes specific examples, it will be apparent toone of ordinary skill in the art that various changes in form anddetails may be made in these examples without departing from the spiritand scope of the claims and their equivalents. The examples describedherein are to be considered in a descriptive sense only, and not ofpurposes of limitation. Descriptions of features or aspects in eachexample are to be considered as being applicable to similar features oraspects in other examples. Suitable results may be achieved if thedescribed techniques are performed in a different order, and/or ifcomponents in a described system, architecture, device, or circuit arecombined in a different manner and/or replaced or supplemented by othercomponents or their equivalents. Therefore, the scope of the disclosureis defined not by the detailed description, but by the claims and theirequivalents, and all variations within the scope of the claims and theirequivalents are to be construed as being included in the disclosure.

What is claimed is:
 1. A method of secure communication in atransmitter, the method comprising: determining whether securecommunication between the transmitter and a receiver is necessary;generating a unique training sequence based on secret information and apublic training sequence, and communicating securely with the receiverusing the unique training sequence, in response to determining thatsecure communication between the transmitter and the receiver isnecessary; and communicating with the receiver using the public trainingsequence shared between the transmitter and the receiver, in response todetermining that secure communication is unnecessary.
 2. The method ofclaim 1, wherein the generating of the unique training sequencecomprises: changing an order of data of the public training sequencebased on the secure communication.
 3. The method of claim 1, wherein thegenerating of the unique training sequence comprises: extracting datafrom the public training sequence selectively based on the securecommunication.
 4. The method of claim 1, wherein the generating of theunique training sequence comprises: combining data of the secretinformation and data of the public training sequence.
 5. The method ofclaim 1, further comprising: determining the secret information suchthat the secret information between the transmitter and the receiver isequal each other.
 6. A non-transitory computer-readable medium embodyinga program executable in a computer device with memory, wherein theexecuted program, when executed, causes the computer device with memoryto perform the method of determining whether secure communicationbetween the transmitter and a receiver is necessary; generating a uniquetraining sequence based on secret information and a public trainingsequence, and communicating securely with the receiver using the uniquetraining sequence, in response to determining that secure communicationbetween the transmitter and the receiver is necessary; and communicatingwith the receiver using the public training sequence shared between thetransmitter and the receiver, in response to determining that securecommunication is unnecessary.
 7. A method of determining secretinformation of a transmitter, the method comprising: transmitting, to areceiver, a hash value generated based on channel information;receiving, from the receiver, a first response corresponding to the hashvalue; changing the channel information of the transmitter such that ahash value of the transmitter generated based on the changed channelinformation is equal to a hash value of the receiver, in response to thetransmitted hash value differing from the hash value of the receiver;and determining the secret information based on the changed channelinformation.
 8. The method of claim 7, further comprising: transmitting,to the receiver, a hash value generated based on the changed channelinformation; and receiving, from the receiver, a second responsecorresponding to the hash value generated based on the changed channelinformation.
 9. The method of claim 8, wherein the determining comprisesdetermining the secret information based on the changed channelinformation in response to the second response indicating that the hashvalue generated based on the changed channel information is equal to ahash value of the receiver.
 10. The method of claim 7, wherein thechanging comprises changing a predetermined length of data of thechannel information.
 11. The method of claim 7, further comprising:quantizing the channel information; and generating the hash value basedon the quantized channel information.
 12. The method of claim 7, furthercomprising: generate a unique training sequence based on the secretinformation.
 13. A method of determining secret information in areceiver, the method comprising: receiving, from a transmitter, a hashvalue of the transmitter; transmitting, to the transmitter, a firstresponse corresponding to the hash value of the transmitter; changingchannel information of the receiver such that a hash value of thereceiver generated based on the changed information is equal to a hashvalue of the transmitter in response to the received hash valuediffering from the hash value of the receiver; and determining thesecret information based on the changed channel information.
 14. Themethod of claim 13, wherein the determining comprises determining thesecret information based on the changed channel information in responseto the second response indicating that the hash value generated based onthe changed channel information is equal to a hash value of thereceiver.
 15. The method of claim 13, wherein the changing compriseschanging a predetermined length of data of the channel information. 16.The method of claim 13, further comprising: transmitting, to thetransmitter, a hash value generated based on the changed channelinformation receiving, from the transmitter, a second responsecorresponding to the transmitted hash value.
 17. A transmitter thatperforms secure communication, the transmitter comprising: at least onehardware processor; and a communicating unit configured to communicatewith a receiver, wherein the at least one processor determines whethersecure communication between the transmitter and the receiver isnecessary, and generates a unique training sequence based on secretinformation and a public training sequence, and communicating securelywith the receiver using the unique training sequence, in response todetermining that secure communication between the transmitter and thereceiver is necessary; and wherein the communicating unit communicateswith the receiver using the public training sequence shared between thetransmitter and the receiver, in response to determining that securecommunication is unnecessary.
 18. The transmitter of claim 17, whereinthe at least one processor changes an order of data of the publictraining sequence based on the secure communication to generate theunique training sequence.
 19. The transmitter of claim 17, wherein theat least one processor extracts data from the public training sequenceselectively based on the secure communication to generate the uniquetraining sequence.
 20. The transmitter of claim 17, wherein the at leastone processor combines data of the secret information and data of thepublic training sequence to generate the unique training sequence. 21.The transmitter of claim 17, wherein the at least one processor generate2 ^(X) unique training sequences, and wherein x is a number of bits ofdata in the public training sequence.
 22. The transmitter of claim 17,wherein the at least one processor generates the unique trainingsequence based on index information of the public training sequence. 23.A transmitter comprising: at least one hardware processor; and acommunicating unit configured to communicate with a receiver, whereinthe communicating unit transmits, to a receiver, a hash value generatedbased on channel information, and receives, from the receiver, a firstresponse corresponding to the hash value of the transmitter, wherein theat least one processor changes the channel information of thetransmitter such that a hash value of the transmitter generated based onthe changed channel information is equal to a hash value of thereceiver, in response to the transmitted hash value differing from thehash value of the receiver, and determines the secret information basedon the changed channel information.
 24. The transmitter of claim 23,wherein the communicating unit transmits, to the receiver, a hash valuegenerated based on the changed channel information, and receives, fromthe receiver, a second response corresponding to the hash valuegenerated based on the changed channel information.
 25. The transmitterof claim 23, wherein the at least one processor determines the secretinformation based on the changed channel information in response to thesecond response indicating that the hash value generated based on thechanged channel information is equal to a hash value of the receiver.26. The transmitter of claim 23, wherein the changing of the channelinformation comprises changing a predetermined length of data of thechannel information.